A court in Thailand has rejected the argument that government plans to amend the constitution are an attempt to overthrow the monarchy.
Lawmakers from the ruling Pheu Thai party see the constitution as undemocratic because it was created after a 2006 army coup.
Their opponents told the Constitutional Court such changes would undermine Thailand's revered monarchy.
The BBC reports that the court, which had tight security amid fears of mass demonstrations, said a referendum was needed to decide whether the government could go ahead with the proposed changes.
A year ago Pheu Thai won more than half the seats in the general election with Yingluck Shinawatra becoming prime minister.
She is the sister of deposed former Prime Minister Thaksin Shinawatra.
Mr Thaksin was ousted by the military in a September 2006 coup and is now living in self-imposed exile in Dubai.
Rivalry between his supporters and opponents, known as red shirts and yellow shirts, has been a frequent cause of political unrest in the country.
Health problems for king
Meanwhile, the country's 84-year-old King Bhumibol Adulyadej, the world's longest-reigning monarch, is experiencing health problems including bleeding in the brain.
But an official statement said his heartbeat and blood pressure were now normal.
The king is revered by many of his subjects and his health is of particular concern because he is seen as a unifying figure in a country that has suffered often violent political upheaval in the past seven years.
The king has been in hospital for almost three years but his health has improved in recent months, allowing him to make a trip to the ancient capital of Ayutthaya in May.